Printed graphics are susceptible to the degratory effects of UV light, rain, ozone, pollution and other external stimulus. In particular, the constant exposure of printed graphics to bright light sources is known to cause serious degradation to the color vibrancy and expected lifetime of the medium. It is well known in the art to overlaminate graphics to protect the images from such natural forces as shown in FIG. 1. Additionally, it is also described in the art that a preferred overlamination medium be constructed of a polyester film overcoated with an adhesive with UV stabilizers imbibed in the adhesive layer. However, the art has failed to provide significantly enhanced stability for the overlamination of graphics output when compared to unstabilized polyethylene terephthalate (PET).
U.S. Pat. No. 5,709,929 describes the construction of a multilayer plastic sheet based upon a cyclohexanedimethanol substituted PET. One layer of the multilayer film is described as containing an UV stabilizer. However the reference fails to teach important requirements for blocking efficiency, film coloration and weatherability necessary for overlamination.
U.S. Pat. No. 5,558,912 describes the stabilization of a cyclohexanedimethanol substituted PET with an UV stabilizer. Again, the reference does not teach the requirements for blocking efficiency, film coloration and weatherability, which is necessary for overlamination.
U.S. Pat. No. 4,446,262 describes the formulation of UV stabilized polymers, but again does not teach the novel requirements for blocking efficiency, film coloration and weatherability, which is necessary for overlamination.
U.S. Pat. No. 4,378,392 describes a multilayer, encapsulating, overlamination film for the enhancement of the longevity of photographs. One embodiment of the overlamination structure describes an UV stabilized PET film. However, it does not teach the novel requirements for blocking efficiency, film coloration and weatherability.
U.S. Pat. No. 4,265,804 describes the formulation of polyester objects having improved weatherability properties, but does not teach the novel requirements for blocking efficiency, film coloration and weatherability, which is necessary for overlamination.
In ISandT NIP13 xe2x80x9cInteractions of inkjet inks with inkjet coatingsxe2x80x9d, pages 430-436, the authors describe the potential value of using UV stabilized overlamination films to improve the longevity of inkjet printed graphics. However, the authors don""t teach the unanticipated value of UV stabilizing a PET film, instead of the adhesive components, to improve longevity of the graphic medium.
Fisher, R. M.; Ketola, W. xe2x80x9cExposure Test Results for Inkjet Inks in Interior Light Environmentsxe2x80x9d in Durability 2000, ASTM-STP 1385.
Bucholz, B. xe2x80x9cNew Performance Standards Sets Durability Guidelines For Industryxe2x80x9d in The Big Picture Conference, 2000, pages 72-73.
PCT WO 00/61664 Describes the formulation of multilayer films with enhanced UV stability properties.
Surprisingly, the inventors have discovered that overlamination films constructed of polyethylene terephthalate (PET), stabilized with specific, sharp boundary transition, UV stabilizers in the PET layer provide a significantly enhanced stability for the over lamination of graphics output when compared to unstabilized PET, or adhesive stabilized overlamination films. This technology is particularly suited for the stabilization of inkjet media output. Specific UV absorbent materials, UVAs, were admixed into PET chip having an intrinsic viscosity (IV) of 0.65. The resultant blend was extruded onto a casting drum to produce a PET sheet of about 1.0 mil thickness. The UVA properties of the polyester films were measured via the use of a Hitachi U-3210 UV/VIS spectrophotometer. UV transmission spectra were taken and the percentage of total transmittance was calculated from 300 nm to 400 nm. The percent transmittance from 300 nm to 400 nm was calculated as an area percent. Therefore, 0 area % would indicate complete cutoff in the range of 300 nm to 400 nm. The transmittance of the films in the visible region, that is greater than 400 nm, was also calculated as an area percentage. The related UV-Vis transmission spectra are plotted in FIGS. 1 and 2.
Test overlamination films were then prepared by handcoating the PET sheets with a light tack acrylic laminating adhesive. These adhesive coated films were then hand laminated against inkjet printed graphics to determine the efficacy of the improvement of the durability of the images.